Two-dimensional convergent/divergent variable area exhaust nozzles with a veer flap extension for added thrust and control during forward flight and a deflector hood for redirecting the exhaust gases downwardly during short or vertical takeoffs are known in the art. One such nozzle is described in U.S. Pat. No. 3,979,067 to D. O. Nash. In that patent the forward thrust gas flow path is formed between a pair of upper flaps and a lower ventral flap. The upper flaps comprise an upstream flap, which pivots about a fixed axis at its upstream end, and a downstream flap which pivots about a fixed axis at its downstream end. The rear end of the upstream flap is joined to the forward end of the downstream flap by a cam and roller connection which allows that joint to move toward and away from the engine axis to vary the nozzle throat. One drawback to this arrangement is that the diverging angle of the downstream flap gets considerably steeper as the nozzle throat area becomes smaller. This may limit the possible turndown ratio (maximum throat area to minimum throat area) due to the boundary layer separating from the downstream flap.
The ventral flap of the Nash nozzle provides throat area control during both forward and vectored thrust. However, since the hood and ventral flap pivot about the same axis, the ventral flap defines an essentially constant (i.e., unvarying) throat area between itself and the hood for all hood positions during thrust vectoring. This is an undesirable limitation.
Other patents which may be of more general interest as regards the state of the art are: U.S. Pat. No. 2,969,641 which shows translating/pivoting flaps for a three-dimensional nozzle for an outer annular secondary air flow; U.S. Pat. No. 3,367,579 which shows free floating translating/rotating divergent flaps for a three-dimensional convergent/divergent nozzle; and, U.S. Pat. No. 4,000,854 which shows a two-dimensional variable area convergent/divergent nozzle having an upper downstream flap pivotally connected at its forward end to the rearward end of a converging upstream flap, and having its rearward end pivotally connected to the downstream end of an outer airplane flap whose movement controls the angular orientation of the downstream flap. None of the foregoing utilize deflector hoods for thrust vectoring. A ventral-type flap which both translates and rotates to vary the throat area of a two-dimensional nozzle is shown in U.S. Pat. No. 4,013,226 to C. M. Willard.